To make batter: Shift together gram flour, rice flour, turmeric powder, baking powder, salt and chilli powder into a bowl and add water stirring constantly to make a smooth batter.
Keep aside for 15 minutes.
Peeled the boil potatoes and while still hot, slightly mashed so that some small pieces remain.
Add chopped ginger, garlic, coriander leaves, salt, sugar, lemon juice and turmeric powder to mashed potato and mix well.
Hit oil in a pan on medium heat.
Add mustard seeds. When cracking, add cumin seed and curry leaves. Stir fry for a few seconds then add asafoetida.
Add to potato mixture and mix well.
Make 12 balls 4 cm in diameter.
To fry wadas, heat oil in a pan on high heat.
Roll 4 balls in batter to coat.
Add one after the other to hot oil and reduce heat to medium.
Fry till light golden brown.
Remove and drain.
Fry the remaining balls in the same way, increasing heat after each batch.
Sprinkle some black salt over it and Serve hot with hot and sweet tomato sauce.
